Basics of broadband impedance spectroscopy measurements using periodic excitations

Measuring the impedance frequency response of systems by means of frequency sweep electrical impedance spectroscopy (EIS) takes time. An alternative based on broadband signals enables the user to acquire simultaneous impedance response data collection. This is directly reflected in a short measuring time compared to the frequency sweep approach. As a result of this increase in the measuring speed, the accuracy of the impedance spectrum is compromised. The aim of this paper is to study how the choice of the broadband signal can contribute to mitigate this accuracy loss. A review of the major advantages and pitfalls of four different periodic broadband excitations suitable to be used in EIS applications is presented. Their influence on the instrumentation and impedance spectrum accuracy is analyzed. Additionally, the signal processing tools to objectively evaluate the quality of the impedance spectrum are described. In view of the experimental results reported, the impedance spectrum signalto- noise ratio (SNR Z) obtained with multisine or discrete interval binary sequence signals is about 20-30 dB more accurate than maximum length binary sequence or chirp signals. © 2012 IOP Publishing Ltd